4.4　Concrete Works

4.4.1　The concrete of the foundation slab shall be placed in layers.And the placing work shall be continuous，and completed at one time.

When the circumferential shell concrete is placing，concrete shall be uniformly placed in layers along the circumference of the circular shell.When there is an underground flue，the concrete for both sides of the flue shall be placed symmetrically.

4.4.2　The positions of construction joints for the foundation shall be in accordance with the following requirements（Figure 4.4.2）:

Figure 4.4.2　locations of construction joints for the foundation

1-Shell；2-Circumferential shell；3-Slab；4-Circumferential beam；5-Shaft；6-Circular slab；A-A Construction joint

1　Construction joints for circular-shaped and round-shaped slab foundations may be at where the foundation slab and circumferential shell are connected.

2　The concrete placing work for the shell foundation shall be continuously completed by horizontal layers at one time.And there shall be no construction joints.When the construction is really difficult to carry out，the constructor shall consult with the designer and supervisor to determine the positions of construction joints.

4.4.3　The construction for massive concrete shall be in accordance with the following requirements:

1　For the massive concrete foundation，the temperature stress of the core concrete shall be determined by calculation.The measures for concrete placing and curing shall be determined in accordance with the calculation result.

2　The mixing ratio shall be properly designed.The efficient plasticizers and mineral admixtures shall be added，and the amount of cement shall be reduced.The continuous grading coarse aggregate shall be used.The clay content and fine content shall not exceed 1%.The clay content of sand shall not exceed 3%.

3　The pozzolanic Portland cement，slag Portland cement and those cements with low hydration and long solidification time shall be chosen.

4　Measures shall be taken to reduce the temperature of the concrete being placed into forms.Concrete may be placed in layers or with the thin-layer-develop technology.The concrete placing time and pace shall be controlled.At the condition of no cold joints，the placing area may be expanded，and reduce the concrete internal temperature.In the process of placing，the rough rubble may be added，which shall not be more than 15%.The strength of the rough rubble shall not be less than the strength of coarse aggregates of concrete.The rough rubble surface shall be free of dirt.

5　The temperature shall be monitored.The measurement points shall not be less than three groups.There shall not be less than three measurement points at different depth of each group.The distance between each group shall be determined in accordance to the actual situation.The monitoring and recording work shall be taken by specific person.The temperature measurement may be carried out with thermometers or sensors.Thermometers or sensors shall be checked before use.

The temperature difference between the core and surface shall not exceed 25℃.The pace of cooling down shall not exceed 1.5℃/d.

6　The insulating and moisturizing methods shall be taken for concrete curing.The thickness of the insulation shall be determined by temperature parameters.Backfill work shall commence immediately after forms is removed.

7　Concrete for the circumferential shell shall be placed during the early cooling down period of foundation slab concrete.